The present invention relates to automatic heat detection and, more particularly, to a method for fluid pressure analytical electronic heat and fire detection, and a corresponding heat detector, used for detecting excessive heat and fire.
Automatic heat detection methods, devices, and systems are implemented for detecting spontaneous occurrence of overheating or excessive heat generation in general, and in particular, when the heat is associated with or caused by a fire. Currently used methods and equipment for automatically detecting a fire are based on detecting different phenomena related to the fire, such as the presence of smoke, radiation, or excessive heat. A first example involves detecting the presence of smoke, by a smoke detector, as the result of something burning, which is normally quite effective for indirectly indicating the presence of a fire. A second example involves detecting radiation emitted by the flames of a fire, by radiation absorption or electro-optical techniques, which are also effective for indirectly indicating the presence of a fire. A third example, involves detecting the occurrence of excessive heat, by a heat detector, directly associated with and at the location of the fire itself, or, caused by the fire but at a distance from the actual fire.
A given fire detector operating with a fire detection mechanism for detecting a fire according to one of the above described types of fire related phenomena is limited to the design and operation of that particular fire detection mechanism. For example, a smoke detector features a smoke detection mechanism for detecting the presence of smoke, which is not designed for, nor capable of, detecting other fire-related phenomena of radiation or excessive heat. A radiation detector features a radiation detection mechanism for detecting emitted radiation, which is not designed for, nor capable of, detecting smoke or excessive heat. Similarly, a heat detector features a heat detection mechanism for detecting excessive heat, which is not designed for, nor capable of, detecting smoke or radiation. Each type of fire detector has particular advantages and disadvantages, usually defined by the characteristics, requirements, and environmental conditions of a particular fire detection application.
Compared to using a heat detector for detecting a condition of excessive heat or fire, there are several specific disadvantages of using fire detectors based upon detecting the other fire related phenomena of smoke and radiation. In particular, proper operation of a smoke or radiation type fire detector strongly depends upon the detection mechanism being located in an area or environment having minimal amounts of interferences such as non-fire related smoke or radiation, fumes of smoke, vapor, or gas, oil, dust, and dirt.
For example, activated mechanical equipment such as running engines, motors, and industrial machinery, are typically accompanied by generation of such interferences. The presence of such interferences can cause malfunction or even non-function of a smoke or radiation type fire detector, leading to a potentially hazardous situation. Moreover, as a result of the affects of interferences, smoke and radiation type fire detectors are typically limited to indoor or other environmentally favorable applications. In general, the above described types of non-fire related interferences minimally influence the performance of heat detectors operating with a mechanism for detecting heat. Accordingly, heat detectors based on detecting excessive heat or fire usually perform more accurately and reliably in applications involving unfavorable environmental conditions, such as in the immediate vicinity of running engines or in outdoor applications.
Another significant disadvantage of using a smoke or radiation type fire detector relates to the response time required for detecting a condition of excessive heat or fire. Based on the fact that smoke and radiation type fire detectors are ordinarily not capable of properly functioning at ground zero `hot` points of excessive heat or fire generation, whereas there are specific types of heat detectors capable of being located and fully functional at such `hot` points, response time to a condition of excessive heat or fire is usually shorter for those types of heat detectors.
The UL 521, Heat Detectors For Fire Protective Signaling Systems, Underwriter Laboratories Inc., IL, USA, seventh edition, 1999, classifies heat detection methods and heat detectors according to a list of various characteristics relating to the type of heat detection mechanism, and according to the physical site, location, or configuration of detection by the heat detection mechanism. Each type of heat detector typically has advantages and disadvantages. Ultimately, the type of heat detector used in a particular application is selected according to specific characteristics, environmental conditions, and requirements of the application.
With respect to the type of heat detection mechanism, a heat detection mechanism is of either an electronic type or non-electronic type. An electronic type heat detection mechanism indicates that electronic circuitry, featuring operation of a single electronic component such as a resistor, or featuring design and cooperative operation of several active and/or passive electronic components on a printed circuit board, is used for responding to a condition of excessive heat or fire, for example, by electronically monitoring temperature and/or rate of temperature rise.
A non-electronic type heat detection mechanism typically features a simple electrical contact, connection, or switch, which is closed by melting of heat sensitive wire insulation, for example, in the case of a thermal or heat-sensitive cable heat detector, or, by actuation of a mechanical mechanism such as a valve, switch, membrane, or diaphragm, for example, in the case of a pneumatic, or gas pressure, type heat detector, where the mechanical mechanism is actuated by an increase in gas pressure due to a rise in temperature as a result of a condition of excessive heat or fire. Typically, a non-electronic type heat detection mechanism is connected to separate electronic circuitry for activating a warning or alarm signal indicating a condition of excessive heat or fire, where the electronic circuitry is not itself involved in detecting or responding to the condition of excessive heat or fire.
Electronic type heat detection mechanisms are generally more adjustable, sensitive, and robust, than non-electronic mechanisms. Electronic type heat detection mechanisms are readily adjustable for high sensitivity, and therefore quick responsiveness, to a condition of excessive heat or fire. Moreover, electronic type heat detection mechanisms are highly robust in that they can be applied at locations having widely varying environmental conditions, whereby the detection mechanism accurately and reproducibly functions with minimal interference by normal variation of environmental conditions. For example, variations in temperatures and pressures, not corresponding to excessive heat or fire in the immediate vicinity of a non-electronic heat detection mechanism, can interfere with and limit proper functioning of a non-electronic type heat detector, causing the heat detector to provide a false warning or alarm signal.
Electronic and non-electronic types of heat detection mechanisms can be operated according to a fixed temperature and/or according to a rate of temperature rise. According to the fixed temperature type of operation, the heat detector features a heat detection mechanism, which, upon detecting a temperature at or above a pre-determined threshold level, is responsive for providing a warning or alarm signal. According to the rate of temperature rise type of operation, the heat detector features a heat detection mechanism, which, upon detecting a rate of temperature rise at or above a pre-determined threshold level, is responsive for providing a warning or alarm signal. A heat detector can be designed and operated according to both a fixed temperature and according to a rate of temperature rise, by featuring a heat detection mechanism adjusted to be responsive to a temperature at or above a pre-determined threshold level and/or to a rate of temperature rise at or above a pre-determined threshold level.
Rate of temperature rise heat detectors are generally more robust than fixed temperature heat detectors, with respect to performance accuracy and reproducibility. Firstly, rate of temperature rise heat detectors are usually electronic, thereby featuring the advantages of operating with an electronic heat detection mechanism. Secondly, detecting a rate of temperature rise above a pre-determined threshold level is considered more accurate than detecting a fixed temperature above a pre-determined threshold level, with respect to identifying a condition of excessive heat or fire.
Heat detectors whose heat detection mechanism operates according to one of either detecting excessive heat, or, detecting flames or fire, are characterized as being single mode. Heat detectors whose heat detection mechanism operates according to detecting excessive heat and/or detecting fire, are characterized as being dual mode. A given single mode or dual mode heat detector can be operated according to a fixed temperature and/or according to a rate of temperature rise. In general, dual mode type heat detectors are more accurate and reliable than single mode type detectors, due to the simultaneous capability of detecting two fire related characteristics of excessive heat and/or fire.
A restorable heat detector features a heat detection mechanism, which, upon detecting and responding to a condition of excessive heat or fire, is not irreversibly damaged or destroyed, in contrast to the heat detection mechanism of a non-restorable heat detector. Restoration or re-setting of the heat detection mechanism of a restorable heat detector may be manual or automatic, where an automatically restorable heat detector is known as a self-restoring heat detector. An example of a non-restorable heat detector is a heat sensitive cable type heat detector which operates by excessive heat or fire melting a heat sensitive coating over wires. This type of heat detector is limited in that upon melting of the coating, the heat detection mechanism is destroyed.
With respect to the physical site or location of detection by the heat detection mechanism, a heat detector is of either a spot type or a line, or linear, type. A spot type heat detector features a heat detection mechanism physically concentrated or located at a particular location or spot, and detects a condition of excessive heat or fire only at that particular location or spot. This is in contrast to a line, or linear, type heat detector which features a heat detection mechanism continuously located along a path, and detects a condition of excessive heat or fire continuously along the entire path. The heat detection mechanism of a line or linear type heat detector can be considered as a continuous series of spot type heat detection mechanisms, with respect to detecting a condition of excessive heat or fire.
A line-type heat detector is typically more versatile and responsive than a spot type detector. One advantage of a line-type heat detector over a spot type heat detector is that of featuring a higher density of excessive heat or fire detection. The physical range of heat or fire detection by a line-type heat detector can be made to be significantly larger than the detection range of a spot type heat detector. In particular, a line-type heat detector is not limited by the heat detection mechanism being located at a single spot in a give location, such as on the ceiling or wall of a room.
A second advantage of a line-type heat detector relates to response time by which a heat detector responds to a condition of excessive heat or fire. A spot type heat detector normally requires significantly longer times for reaching an activated state of responding to excessive heat or fire, due to the time required for heat transfer from ground zero `hot` points of the excessive heat or fire to the location of the spot type heat detection mechanism, whereas, a line-type heat detector operating with a higher density of excessive heat or fire detection, usually has its heat detection mechanism located closer to, or even at, ground zero `hot` points of the excessive heat or fire.
For example, in the event of a condition of excessive heat or fire occurring at or near an activated engine or piece of machinery, in the case of a line-type heat detector, the excessive heat or fire is quickly detected because the line-type heat detection mechanism is typically in physical contact with the engine or machinery, in contrast to a spot type heat detection mechanism which is typically located a distance away from the engine or machinery, requiring significantly more time for responding to the condition of excessive heat or fire. Moreover, a spot type heat detection mechanism usually requires a condition of fire, and not just of excessive heat, for activation, which, by the time the spot type heat detector is activated, there may develop a more serious or hazardous situation. For example, in scenarios like the one just described, a line-type heat detector can actually lead to saving a burning engine or piece of machinery, whereas using a spot type heat detector in the vicinity of the engine or piece of machinery will probably result in complete burning, or irreversible damage, of the engine or machinery, prior to potentially saving it.
A third advantage is that a line-type heat detector is usually more applicable to environmental conditions unfavorable to properly detecting a condition of excessive heat or fire. A line-type heat detection mechanism can readily be located in an area or environment, for example, near activated mechanical equipment such as running engines, motors, and industrial machinery, typically associated with significant amounts of smoke, radiation, fumes of smoke, vapor, or gas, oil, dust, and dirt, which, near the detection region of a spot type heat detector may interfere with proper operation of the heat detection mechanism, causing malfunction or even total inactivation of the spot type heat detector, ultimately leading to a potentially hazardous situation.
There are currently available different types of heat detectors, each featuring either a non-electronic or an electronic type of heat detection mechanism, where the heat detection mechanism is based on, for example, heat or thermal sensitivity, or, pneumatics. Furthermore, as described above, each of these heat detection mechanisms can operate according to a fixed temperature and/or according to a rate of temperature rise.
A first example is a heat or thermally sensitive cable non-electronic line-type heat detector, operating according to a fixed temperature, which, aside from featuring previously described advantages of line-type heat detectors, is limited by being non-electronic, and by the cable typically being sensitive to environmental effects such as mechanical contact, shock, bending, and squeezing. Moreover, this kind of line-type heat detector is non-restorable due to destruction of the cable upon detection of a condition of excessive heat or fire.
A second example is a heat or thermally sensitive resistance electronic line-type heat detector, operating according to a fixed temperature, whereby resistance of a resistor decreases with increasing temperature, up to a fixed temperature, causing the shorting, or closing, of a circuit in the heat detection mechanism for responding to a condition of excessive heat or fire. This line-type heat detector has several disadvantages, such as the need for the resistor in the heat detection mechanism to generate a significant quantity of heat in order to respond to temporal changes in temperature associated with that of excessive heat or a fire, response time is relatively slow for an electronic line-type heat detector, and is limited to indoor use.
A third example is the category of pneumatic non-electronic heat detectors, including spot type and line-type pneumatic heat detectors, where the heat detection mechanism operates according to a fixed temperature and/or a rate of temperature rise. A pneumatic non-electronic heat detector features a pneumatic non-electronic heat detection mechanism which operates according to changes in gas pressure due to changes in temperature, and for a gas pressure, or rate of gas pressure rise, above a pre-determined threshold level, corresponding to a temperature, or rate of temperature rise above a pre-determined threshold level, respectively, there is actuation of a mechanical mechanism, involving movement of a valve, switch, membrane, or diaphragm, effecting closure of an electrical contact, connection, switch, or electronic circuit, followed by activation of a warning or alarm signal for indicating a condition of excessive heat or fire.
In a pneumatic non-electronic heat detector, the pneumatic non-electronic heat detection mechanism may be either closed or open, with respect to an external source of gas, for example, ambient atmosphere. In a closed pneumatic non-electronic heat detector, an enclosed internal volume of gas is closed to any external source of gas, such as ambient atmosphere. In an open pneumatic non-electronic heat detector, there is included at a particular location along the enclosed volume of gas a small passageway open to an external source of gas, usually configured and functioning as a gas flow restrictor, for example, an open capillary tube or orifice, for enabling equilibration of internal gas pressure with the external source of gas pressure, thereby, enabling compensation of variations in internal gas pressure due to normal variations in the temperature of the environment being monitored for a condition of excessive heat or fire.
A significant general limitation of currently available pneumatic non-electronic heat detectors, including closed or open types, spot types or line-types, operating according to a fixed temperature and/or rate of temperature rise, is that they are non-electronic, whereby operation of the particular heat detection mechanism is based on actuation of a mechanical mechanism, involving movement of a valve, switch, membrane, diaphragm, or similar actuatable device featuring one or more moving parts, for effecting closure of an electrical contact, connection, switch, or electronic circuit. Moreover, a pneumatic non-electronic heat detection mechanism typically requires a significant level of gas pressure in order cause actuation of the one or more moving parts.
Furthermore, the pneumatic non-electronic heat detection mechanism responds to, but cannot analyze, a potential or possible, condition of excessive heat or fire. A pneumatic non-electronic heat detection mechanism is not capable of analyzing the pneumatics, or the mechanics, of the actuation of the mechanical mechanism. Once actuation of the mechanical mechanism is complete, proper operation of a pneumatic non-electronic heat detection mechanism irreversibly leads to effecting a warning or alarm signal indicating a condition of excessive heat or fire, regardless of the condition of excessive heat or fire being actual or not, or, in logic terms, true or false. As such, a pneumatic non-electronic heat detection mechanism may respond to false conditions of excessive heat or fire, caused by a variety of reasons.
Accordingly, accuracy and reproducibility of pneumatic non-electronic heat detectors are directly related to, and totally dependent upon, the accuracy and reproducibility of the process of actuating the mechanical mechanism, and therefore, of operation of the one or more moving parts. Clearly, sufficient interference or failure in proper actuation or operation of the mechanical mechanism precludes proper functioning of the heat detection mechanism, consequently resulting in such a heat detector either responding to false conditions of excessive heat or fire, performing below specifications, or not performing at all, leading to a potentially hazardous situation.
Further, with respect to an open pneumatic non-electronic heat detector, its performance level is determined by the extent to which variations in the internal gas pressure are accurately and reproducibly compensated for by equilibration with atmospheric pressure. This feature limits applicability of an open pneumatic non-electronic heat detector in two specific ways, as explained here.
First, a properly designed, calibrated, and adjusted open pneumatic non-electronic heat detection mechanism with respect to a particular atmospheric pressure is still vulnerable to variations in the atmospheric pressure outside of the calibration range, adding a degree of unpredictability, and potentially causing malfunction, of the heat detector. For example, spontaneous and/or transient change in magnitude and/or direction of air movement in the immediate vicinity of the heat detection mechanism can cause spontaneous and/or transient spikes or dips in the enclosed volume internal gas pressure outside of the calibration range, possibly causing undesirable activation of the warning or alarm signal, falsely indicating a condition of excessive heat or fire.
Second, an open pneumatic non-electronic heat detector, is limited during conditions of very slow development of a condition of excessive heat or fire, during which the pneumatic non-electronic heat detection mechanism can self-calibrate or compensate itself to the slowly varying external conditions associated with the slowly developing excessive heat or fire. Accordingly, the pneumatic non-electronic heat detection mechanism may not distinguish the actual developing condition of excessive heat or fire from normally varying external environmental conditions. Such a realistic scenario can result in a slowly developing condition of excessive heat or fire going undetected, clearly leading to a hazardous situation.
Proper design and manufacturing of a heat detector according to established industry standards ordinarily includes a standard test procedure and additional heat detector components, mechanisms, and/or peripheral equipment for automatically testing the performance of the heat detection mechanism, and therefore, the heat detector. Automatically testing the performance of a pneumatic non-electronic heat detector is currently accomplished by using a separate electro-mechanical mechanism for artificially stimulating and causing actuation, for example, by increasing pneumatic pressure, of the mechanical mechanism of the heat detection mechanism, for effecting closure of the electrical contact, connection, switch, or electronic circuit, for activating a test warning or alarm signal indicating a test condition of excessive heat or fire.
Similar to limitations associated with normal operation of a pneumatic non-electronic heat detector, the standard automatic testing procedure is also limited by depending upon accurate and reliable functioning of the additional electro-mechanical mechanism, involving movement of a valve, switch, membrane, diaphragm, or similar actuatable device featuring one or more moving parts, as part of the artificial stimulus for increasing pneumatic pressure in the heat detector. Similarly, sufficient interference or failure in proper actuation or operation of the electro-mechanical mechanism during the automatic test procedure precludes proper functioning of the heat detection mechanism during the automatic test procedure. For example, a malfunctioning electro-mechanical mechanism can incorrectly effect closure of the electrical contact, connection, switch, or electronic circuit, for falsely activating a test warning or alarm signal, thereby falsely indicating a test condition of excessive heat or fire. This results in incorrectly, or falsely, determining proper performance of such a heat detector, leading to a potentially hazardous situation.
Another disadvantage of the current standard procedure for automatically testing the performance of a pneumatic non-electronic heat detector is that it involves artificially, not naturally, stimulating or causing actuation of the mechanical mechanism of the heat detection mechanism, for effecting closure of the electrical contact, connection, switch, or electronic circuit, for activating a test warning or alarm signal indicating a test condition of excessive heat or fire.
Artificially, and automatically, stimulating or causing actuation of the mechanical mechanism of a pneumatic non-electronic heat detection mechanism is typically done by using the previously mentioned electro-mechanical mechanism, provided in the heat detector at the time of its manufacture. Upon prompting the electro-mechanical mechanism by an end-user, such as by pushing a button or turning a switch of an electrical circuit, the electro-mechanical mechanism generates an increase in gas pressure in the enclosed volume of the heat detection mechanism sufficient to cause actuation of the mechanical mechanism of the heat detection mechanism, for effecting closure of the electrical contact, connection, switch, or electronic circuit, for activating a test warning or alarm signal indicating a test condition of excessive heat or fire.
In contrast, naturally stimulating or causing natural actuation of the mechanical mechanism of a pneumatic non-electronic heat detection mechanism would involve supplying sufficient heat or fire to the heat detection mechanism, thereby naturally increasing the gas pressure in the enclosed volume of the heat detection mechanism, causing actuation of the mechanical mechanism of the heat detection mechanism, for effecting closure of the electrical contact, connection, switch, or electronic circuit, for activating a test warning or alarm signal indicating a test condition of excessive heat or fire. Given the choice, a private user of a single heat detector, or, a fire prevention officer of a large facility having many heat detectors, would be expected to prefer subjecting a heat detector to test conditions as close as possible to actual conditions of excessive heat or fire, such as by naturally stimulating or causing natural actuation of the heat detection mechanism for indicating a test condition of excessive heat or fire.
A few prior art references featuring specific types of heat detectors described above are herein provided. Limitations associated with each heat detector device are only briefly listed here, with a more detailed understanding obtainable by referring to the above discussion.
In EP Patent No. 350440, issued to Securiton AG, a pressure surveillance device for a temperature detector is disclosed. Consistent with above described terminology, the device features an open pneumatic non-electronic line-type heat detection mechanism operating according to a rate of temperature rise. Warming of a sensor tube filled with air at a rate above a pre-determined threshold level causes actuation of a movable membrane for effecting closure of an electrical switch, followed by activation of a warning or alarm signal for indicating a condition of excessive heat or fire. A capillary tube is included in the device for enabling compensation of variations in internal gas pressure not related to a condition of excessive heat or fire. Automatic testing of the device is performed by using a bellows, a pressure sensor, a membrane switch, and a valve, for artificially causing actuation of the mechanical mechanism of the heat detector mechanism.
In U.S. Pat. No. 4,651,140, issued to Duggan, a fire detector is disclosed, which features an open pneumatic non-electronic heat detection mechanism. The heat detection mechanism can be operated as either a fixed temperature or a rate of temperature rise type, involving actuation of a moveable diaphragm for effecting closure of an electrical circuit, followed by activation of an alarm signal for indicating a condition of excessive heat or fire. A vent aperture is included in the device for enabling compensation of variations in internal gas pressure not related to a condition of excessive heat or fire.
Limitations of the heat detectors described in the preceding disclosures relate to the heat detection mechanism operating as open and non-electronic, including the need for actuating a movable membrane or diaphragm for closing an electrical switch. Moreover, the automatic testing procedure disclosed in EP Patent No. 350440, features artificial, not natural, actuation of the mechanical mechanism of the heat detector mechanism, and is further limited by requiring concerted movement of several mechanical components.
In U.S. Pat. No. 5,136,278, filed Mar. 15, 1991, by Watson et al., a pneumatic pressure detector for fire detection is disclosed, which features a closed pneumatic non-electronic line-type heat detection mechanism operating according to a fixed temperature. The heat detection mechanism features a closed capillary type sensor tube which has absorbed in it a gas. The gas expands upon an increase in temperature associated with a condition of excessive heat or fire, actuating a first deformable diaphragm for effecting closure of an electrical switch, followed by activation of an alarm signal. A low pressure activated switch and a second deformable diaphragm are included in the device for enabling compensation of a drop in internal gas pressure below a specified level. Limitations of the disclosed pressure detector relate to the heat detection mechanism operating as non-electronic, including the need for actuating the first deformable diaphragm for closing an electrical switch, and requiring concerted movement of the low pressure switch and the second deformable diaphragm for compensating a drop in internal gas pressure.
To one of ordinary skill in the art, there is thus a need for, and it would be highly advantageous to have a method for fluid pressure analytical electronic heat and fire detection, and a corresponding heat detector, used for detecting excessive heat and fire. Moreover, it would be highly advantageous to have such a method and corresponding heat detector featuring an analytical electronic heat detection mechanism having no moving component, such as a valve, switch, membrane, diaphragm, or similar actuatable device of one or more moving parts, for first analyzing a potential condition of excessive heat or fire, followed by logical and definitive determination of an actual condition of excessive heat or fire, for effecting activation of a warning or alarm signal indicating an actual condition of excessive heat or fire. Furthermore, it would be advantageous to be able to implement such a method and corresponding heat detector in a variety of applications, encompassing a wide range of environmental conditions, in a cost effective manner.